1. Field of the Invention
The present invention relates to an exposure apparatus which scans both a substrate such as a wafer and an original such as a reticle to expose and transfer a pattern on the reticle onto the wafer substrate, a control method for the same, and a device manufacturing method.
2. Description of the Related Art
An exposure apparatus to manufacture a semiconductor integrated circuit is desired to simultaneously cope with a high integration density and improve the number of wafers to expose per unit time, that is, the throughput, thereby providing a more inexpensive chip. To satisfy these demands, currently, is most popular to use a scanning exposure apparatus. This apparatus projects only a rectangular band-like region of a pattern on a reticle onto a wafer substrate or the like, and scans both the reticle and wafer substrate in a sync manner to transfer the entire pattern onto the wafer substrate. This exposure apparatus has a reduced projection system with a magnification of ¼ to ⅕, limits the irradiation region of exposure light to a rectangular band-like region, and is provided with a stage which scans the reticle and wafer substrate with a speed ratio equal to the reduction magnification of the reduced projection system.
FIGS. 6 and 7 are respectively an upper perspective view of a general scanning exposure apparatus and its sectional view taken along a Y-Z plane. This exposure apparatus has an exposure light source and an optical illumination system (neither is shown), and a reticle stage 100, reduced projection system 110, and wafer stage 120.
The reticle stage 100 includes a base 101, a table 103 for mounting a reticle 104 thereon, and linear actuators 105 such as linear motors. The linear actuators 105 reciprocally move the table 103 on the base 101 in the Y direction. The wafer stage 120 includes a base 121, a table 127 for mounting a wafer substrate 128 thereon, and linear actuators 123 such as linear motors. The linear actuators 123 reciprocally move the base 121 on the base 121 in both the X and Y directions.
The reduced projection system 110 is fixed to a lens barrel supporting member 111. Laser interferometers 106 and 130 are fixed to the lens barrel supporting member 111 through support pillars. Mirrors (not shown) set on the tables 103 and 127 respectively reflect laser beams coming from the laser interferometers 106 and 130 to measure the positions of the reticle stage 100 and wafer stage 120. The position measurement results are respectively fed back to the linear actuators 105 and 123.
The linear actuators 105 and 123 respectively, reciprocally move the reticle stage 100 and wafer stage 120 on the bases 101 and 121. During pattern exposure of the reticle 104 with exposure light, the scanning speeds of the reticle stage 100 and wafer stage 120 are controlled to be constant.
The scanning exposure apparatus as described above faces a demand, which becomes stronger every year, of further improving the throughput to increase the productivity. To meet this demand, Japanese Patent Laid-Open No. 2004-79639 discloses a moving stage apparatus in which, to enable a reticle stage to move at a higher speed, repulsion members made of magnets are set at the stroke ends of the stage, thereby generating a large thrust and maintaining the high speed.
FIGS. 8A and 8B show the arrangement of this conventional moving stage apparatus. As shown in the plan view in FIG. 8A, a base guide 132 is fixed to a main body base 131. The base guide 132 supports a table 134 for mounting a work 133 thereon such that the table 134 is movable in one direction with respect to the base guide 132.
Bearings 144 arranged between the upper surface of the base guide 132 and the lower surface of the table 134 regulate the posture of the table 134. A semiconductor exposure apparatus for which high-accuracy alignment is required employs air bearings as the bearings 144. Linear motor movable elements 135 are fixed on the two sides of the table 134. Linear motor stators 136 face the linear motor movable elements 135 in a non-contact manner. Each linear motor stator 136 is fixed to the main body base 131 through legs 137 at two ends. The position of the table 134 is measured as a laser interferometer radiates light to a mirror 146.
This moving stage apparatus comprises repulsion magnet units each as shown in FIG. 8B. Repulsion movable elements 147 each comprising a movable magnet holder 138 and movable magnet 139 are fixed in front of and behind the table 134. The movable magnet 139 is a plate-like unipolar permanent magnet magnetized in the vertical direction. In this prior art, the upper side of the movable magnet 139 is magnetized as an N pole. The repulsion movable elements 147 serve as insertion magnets and react with corresponding repulsion stators 140 arranged on the base guide 132 to apply repulsion forces to the table 134, thereby accelerating and decelerating the table 134.
In each repulsion magnet unit, upper and lower magnets 142 sandwich the respective magnetic pole surfaces of the movable magnet 139 from the two sides to cancel the repulsion forces in the opposing directions. To correspond to the repulsion movable elements 147, the repulsion stators 140 which accelerate or decelerate the table 134 are fixed on the base guide 132. The repulsion stators 140 are arranged one unit at each end of the stroke of the table 134.
Each repulsion stator 140 forms a set magnet comprising an upper yoke 141, the upper magnet 142, horizontal yokes 143 on two sides, the lower magnet 142, and a lower yoke 141. The upper and lower magnets 142 are plate-like unipolar permanent magnets magnetized in the vertical direction, in the same manner as the repulsion movable elements 147. Note that the magnets 142 are arranged such that the same polarity poles face the same polarity poles of the repulsion movable element 147. More specifically, the magnets 142 are arranged such that the lower surface of the upper magnet 142 is an N pole and that the upper surface of the lower magnet 142 is an S pole. The upper yoke 141, horizontal yokes 143, and lower yoke 141 are provided so that the magnetic fluxes of the upper and lower magnets 142 circulate through them sideways.
The upper and lower magnets 142 are set at a gap slightly larger than the thickness of the repulsion movable magnet 139. The inner gap of the two horizontal yokes 143 is maintained to be larger than the width of the movable magnet 139. Thus, the repulsion movable magnet 139 is inserted in a non-contacting manner in a hole formed by the upper and lower magnets 142 and two horizontal yokes 143.
A stage that uses these repulsion magnet units achieves a higher speed and smaller heat generation.
According to Japanese Patent Laid-Open No. 2004-79639, at one stroke end of the table 134, the movable magnet 139 enters the corresponding repulsion stator 140 to impart a repulsion force against movement of the table 134.
Assume a case wherein a reticle changer to change a reticle automatically is mounted on the exposure apparatus described in Japanese Patent Laid-Open No. 2004-79639. In this case, when changing the reticle, the reticle changer should not interfere with an optical illumination system. Usually, the optical illumination system is arranged at the stroke center of the table 134. The position where the reticle changer changes the reticle is accordingly set at the stroke end side on the table 134.
As described above, the stroke end of the table 134 is the position where the mutual operations of the movable magnet 139 and repulsion stator 140 generate a repulsion force in the table 134. Thus, when changing the reticle, a mechanism to hold the table 134 against the repulsion force is separately necessary, which increases the cost. If such a mechanism holds the table 134 locally, it may deform the movable magnet 139 and table 134, and even a reticle to be placed.